1. Field of the Invention
The present invention relates to pipe cutting operations. More particularly, the present invention relates to an anchoring system for a pipe cutting apparatus by equalizing the forces above and below the cutting portion of the apparatus to prevent movement of the cutting apparatus during cutting operations, and eliminating mechanical anchoring systems and pressure activated button/slip anchor systems.
2. General Background
During drilling or production of oil and gas wells, quite often a string of casing or drill pipe or other tubular members which is downhole cannot be retrieved from the well, due to the string becoming lodged downhole at some point along its length. Therefore, there are devices known in the art which are lowered into the bore of the pipe or casing, and through either chemicals or heat imparted to the pipe or casing wall, the pipe or casing is cut, and the casing or pipe above the cut is removed from the borehole, and the pipe or casing below the cut must remain in the well.
One such device is disclosed and claimed in U.S. Pat. No. 4,598,769, entitled "Pipe Cutting Apparatus," by the same inventor, Michael C. Robertson, which is incorporated herein by reference thereto. One of the features of the device disclosed in the '769 Robertson patent, is the feature of an anchoring system on the device. As in all devices of this type, when the device has been lowered to the desired depth, the device is mechanically anchored within the bore of the pipe or casing with a plurality of jaws which move outward from the tool body and engage the wall of the casing or pipe. The engagement of the jaws against the pipe or casing wall prevents the apparatus from moving within the casing or pipe when the cutting apparatus is fired. Since the device disclosed in the '769 Robertson patent utilizes a chemical reaction to produce the tremendous heat against the pipe in order to burn through the pipe wall, there is produced a volume of gas into the borehole at the point of the cut. This volume of gas, under very high pressure, tends to build up a tremendous upward pressure residing beneath the cutting apparatus. Therefore, were it not for the mechanical anchor system as described above, the force of the gas beneath the apparatus would tend to force the apparatus upward, in the borehole, which is very undesirable. Since this would occur simultaneously with the cutting operation, it would produce a very uneven and jagged cut, and may also be of such magnitude to propel the apparatus out of the borehole, causing damage, and perhaps endangering the safety of the workers on the rig floor.
The shortcomings of the mechanical anchors as is used currently in the art is the fact that the anchors must be set manually and properly prior to firing the mechanism, and therefore, results in preliminary preparation within the borehole prior to the actual cutting operation. Further, because of the mechanical nature of the anchor system, the anchors may not set properly, resulting in movement of the cutting apparatus, or may not function at all, and would require the entire tool to be retrieved from the hole for service.